By Francois Murphy, John Irish and Parisa Hafezi VIENNA (Reuters) -Western powers on Tuesday warned Russia against wrecking an almost completed deal on bringing the United States and Iran back into compliance with the 2015 nuclear accord, as Iran’s top negotiator was set to return from consultations in Tehran. Eleven months of talks to restore the deal which lifted sanctions on Iran in return for curbs on its nuclear programme have reached their final stages. But they have been complicated by a last-minute demand from Russia for guarantees from the United States that Western sanctions targetin…